Of the many forms the malaria parasite takes during its very complex life cycle, three stages must invade host cells, the ookinete, the sporozoite and the merozoite. Without a doubt, many features of the invasion machinery are common among these three stages;however each stage must contain unique features which may be specific for the host cell being invaded. In many cases, the steps of the invasion process are the target of both immunologic and chemotherapeutic intervention to block the spread of malaria. We have initiated studies to study the machinery associated with the process of invasion. Using a well-characterized P. yoelii mixed blood stage cDNA library, we have isolated and characterized a key component (PyMTIP, Myosin A Interacting Protein) of the invasion motor machinery, which has allowed us to propose a new model for the organization of the invasion motor machinery in invading parasites. This work proposes to expand on these initial studies to create a protein-protein interaction network involved in the invasion of erythrocytes by merozoites. Using the recently solved structure of MTIP in combination with a peptide derived from MyoA, we will further characterize the interactions associated with the MTIP molecule and initiate a screen for small molecule inhibitors of the interaction between MTIP and the carboxyl terminal tail of myosin. The approaches will utilize both a yeast-based small molecule library screen and a structure-guided synthetic approach. These studies will provide valuable information in regards to this key step in the life cycle of the malaria parasite and potentially identify new targets and strategies for immunological or chemotherapeutic intervention. Additionally studies are proposed to investigate the role of two molecules specifically defined using a database search of the P. falciparum genome, which are candidates for the receptor that links the cell to be invaded to the actin-myosin motor, which drives invasion. Intriguing results suggest that the molecules are not functionally equivalent in human and rodent malarias and studies are proposed to investigate the molecular basis for these observations. Also, we have identified potential strain- specific expression of one of these molecules in P. falciparum and will determine the genetic basis for this phenomenon. Together these studies will provide key information for our efforts to define the basis of invasion and identified new strategies for intervention against this deadly parasite.